JPH0235575B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention belongs to the technical field of X-ray diagnostic equipment,
In more detail, while giving the contrast agent to the subject.
This invention relates to a dynamic CT device that obtains tomographic images by performing a CT scan.

[Technical background of the invention and its problems]

In recent years, as X-ray CT scanners have become faster, so-called dynamic scans have become available, which track changes in contrast agent concentration in each part of the subject over time by applying a contrast agent to the subject and scanning over time. I'm starting to be able to do it.

In conventional dynamics scanning, as shown in Figure 1, relative image data is used for time-axis analysis (dynamics study) of changes in contrast agent concentration over time at a predetermined region of the subject.
In order to obtain P'(t _k ) (where k=1, 2, ......, n), the detection data output from the X-ray detection system is A/D converted and log converted to obtain data. R
(t _k ) (k = 0, 1, 2, ......, n) to calibration data C (usually water data)
Image reconstruction processing is performed on the projection data obtained by subtracting , and an absolute image P(t _k ) (k=0, 1, 2, . . . , n) is obtained. Note that here, P(t ₀ ) is the data of the tomographic image of the subject when the contrast medium has not yet reached the predetermined site within the subject, and P(t ₁ ), P(t ₂ ) ... is data of a tomographic image (contrast image) of a subject when the contrast medium reaches a predetermined site within the subject and the contrast medium concentration changes over time. Next, the contrast image data P
( _t1 ), P( _t2 )...P(t _o ) to tomographic image data P
(t ₀ ), a series of relative image data P'(t _k ) is obtained.

However, as mentioned above, conventional dynamic scan requires two subtraction processes for each data in addition to the reconstruction process, which not only prolongs the calculation time but also requires limited projection In the segment image, which is reconstructed by interpolating the projection data (180° + fan angle) to create the entire projection data (360° minutes), artifacts that depend on the angular component of the data are removed due to the interpolation process. There is a problem with the fact that it is easy to occur.

[Purpose of the invention]

This invention was made in view of the above circumstances, and it is possible to directly and quickly obtain relative image data, which is the final data required for a dynamics study, and also to remove artifacts of segment images. The purpose is to provide a dynamic CT device.

[Summary of the invention]

To achieve the above object, the present invention is summarized as follows:
Contrast imaging is performed in a dynamic CT device that contrasts a predetermined region of the subject by administering a contrast agent, obtains projection data through an X-ray CT scan, reconstructs an image based on the projection data, and obtains a subtraction image. A first memory stores subsequent projection data, a second memory stores pre-contrast projection data, and a second memory stores the projection data read from the first memory and the projection data read from the second memory. The present invention is characterized by comprising a subtraction means for subtracting excision data and using the obtained subtraction data for image reconstruction.

[Embodiments of the invention]

FIG. 2 is a schematic block diagram showing one embodiment of the present invention.

In FIG. 2, the reference numeral 1 indicates the first switch, which inputs the X-ray data output from the X-ray detection system, and under the control of a controller (not shown),
The configuration is such that input X-ray data is output to a first memory 2, a second memory 3, and a third memory 4 according to its type. The first memory 2 is
Of the X-ray data, data R(t ₁ ), ..., R(t _o ) provides a contrast image when the contrast agent concentration changes over time after the contrast agent reaches a predetermined site within the subject.
This is a frame memory that stores . The second memory 3 is a frame memory that stores, among the X-ray data, data (t ₀ ) that provides a tomographic image before the contrast agent reaches a predetermined region within the subject. The third memory 4 is a frame memory that stores calibration data among the X-ray data. Reference numeral 5 designates a second switch, and under the control of a controller (not shown), the data R(t ₀ ) stored in the second memory 3 and the third memory 4 are changed.
and calibration data is output to the subtracter 6. During normal scan, calibration data is transferred, and during dynamic scan, data R is output.
(t ₀ ) Transfer. From the data R(t ₁ ), R(t ₂ )...R(t _o ) stored in the first memory 2, the subtracter 6 calculates
Data R(t ₀ ) transferred via the second switch 5
It has a configuration that subtracts . Reference numeral 7 denotes an image reconstruction device, which has a configuration for reconstructing a subtraction image using data output from the subtractor 6. 8 is a fourth memory, which stores data P'(t ₁ ), P'(t ₂ ), ...P'(t _o ) giving subtraction images output from the image reconstruction device 7. It is a memory that stores.

With the above configuration, among the X-ray data output by the X-ray detection system, the X-ray data that gives a contrast image is stored in the first memory 2, and the data that gives a tomographic image before the contrast agent reaches is stored in the first memory 2. 2, and then the subtracter 6 stores it in the first memory 3.
Data stored in R(t ₁ ), R(t ₂ )...R(t _o )
The data R(t 0 ) transferred via the second switch 5 is subtracted from the data R(t ₀ ), and the image reconstruction device 7 reconstructs the subtraction image using the data obtained by subtraction. Data P′(t ₁ ), P′(t ₂ ) giving subtraction images when the contrast agent concentration changes...
P'(t _o ) is stored in the fourth memory 8 in preparation for the subsequent dynamics study.

As described above, according to the embodiment, the subtraction image can be reconstructed from the raw data level by using only one subtractor 6, so that data processing can be performed at high speed. Also, the second
The subtracter 6 subtracts the data R(t ₀ ) stored in the third memory 3 and the calibration data stored in the third memory 4, and the image reconstruction device 6 reconstructs an absolute image. Data giving an image P(t ₀ )
If stored in a fifth memory (not shown), data P(t ₀ ) giving an absolute image and data P'(t ₁ ) giving a subtraction image which is a relative image,
By adding P′(t ₂ ), . . . P′(t _o ), data P(t ₁ ), P(t ₂ ), . P(t _o ) can be obtained.

Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment, and can be implemented with appropriate modifications within the scope of the gist of the invention. Needless to say.

In the embodiment described above, what is stored in the first memory 2 and the second memory 3 are the projections obtained when the X-ray tube goes around the outer periphery of the subject around the body axis of the subject. Although it is a yon data,
It may also be projection data that provides segment images. In other words, most of the artifacts that occur in segment images and depend on the rotation angle of the X-ray tube originate from areas that are not changed by the contrast agent. first memory 2
In this method, the X-ray tube is rotated by a predetermined angle, for example, 210 degrees around the circumference of the subject, and the contrast medium concentration changes over time after the contrast medium reaches a predetermined location within the subject. Extraction data R _kl (where k corresponds to the time axis and l corresponds to the rotation angle of the X-ray tube) is stored in the second memory 3.
The subtracter 6 stores projection data R _0l obtained by rotating the X-ray tube by a predetermined angle, for example, 210 degrees around the outer periphery of the test subject before the contrast medium reaches a predetermined part of the test subject. Projection data of the same angle from memory 2 of 1 and memory 3 of second
Read R _kl and R _0l , perform subtraction process of R _kl − R _0l ,
It may also be possible to correct the projection data. In this way, a subtraction image free of artifacts can be reconstructed using segment images at the stage of raw data. It goes without saying that, prior to the reconstruction of the subtraction image, it is necessary to provide the image reconstruction device 7 with an interpolation processing device that interpolates the data of the segment image and generates 360° data.

〔Effect of the invention〕

According to this invention, it is possible to realize high-speed data processing in dynamic scanning with a simple configuration without significantly changing the conventional scanner system. Dynamics that can prevent the occurrence of artifacts
CT equipment can be provided. In addition, in a relative image obtained by dynamic scanning, in which post-contrast data is subtracted from pre-contrast data, artifacts such as shedding due to beam hardening around substances with high X-ray absorption coefficients, such as bones, are almost eliminated. Since this phenomenon rarely occurs, it is possible to provide a dynamic CT apparatus that is highly effective in diagnosing the head, particularly the cerebellum, spinal cord, and the like. moreover,
If the base image before contrast is separately filed, an absolute image can be obtained by simply adding the base image to the contrast image, which is a relative image.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a conventional method for obtaining a subtraction image, and FIG. 2 is a block diagram showing an embodiment of the present invention. 2...First memory, 3...Second memory, 6
...Subtractor.

Claims (1)

[Claims] 1 In a dynamic CT device that contrasts a predetermined region within the subject by administering a contrast agent, obtains projection data through an X-ray CT scan, reconstructs an image based on the projection data, and obtains a subtraction image. , a first memory that can store projection data from a plurality of scans after contrast imaging, a second memory that stores projection data before contrast imaging; A dynamic device comprising a subtraction means for reading and subtracting projection data from a memory, and a reconstruction means for reconstructing an image based on the subtraction data obtained by the subtraction means.
CT device.